Primary Contracted Heels: Causes & Treatment

Contracted heels in the horse is characterized by a shift of the hoof wall
resulting in the narrowing of the foot. Primary cases of contracted heels
result from unbalanced feet, either long toe/low heels (LTLH) or overgrown
hooves. Trimming the feet and correcting the hoof angle result in expansion
of the heels. Secondary contracted heels are caused by lameness and disuse
of the limb, resulting in hoof atrophy.

Problems associated with contracted heels include disruption of the
shock-absorption mechanism of the foot (Rooney 1974). The contracted hoof
wall presses internal structures, a condition termed hoof bound (Rick 1907).
Crevices and grooves formed by the contracting hoof creates a favorable
environment for thrush.

FACTORS LEADING TO LONG TOE/LOW HEEL

Some horses' hooves tend to grow the toe at a faster rate than the heels.

Expansion and contraction of the heels during motion increases their wear
relative to the toe.

(The photo to the left shows typical underrun heels. The heels are dropped,
and the bulb of the heels are prominent. The condition can be caused by a
horseshoe that is too small, as can be seen here.)

Many horses have naturally underrun, weak heels. The heels are lowered more
than necessary, creating a broken foot axis.

CLINICAL APPEARANCE

Initial cases of primary contracted heels are not lame. Any foot can become
affected, but the condition is more common in the forelegs. The hoof appearance
is similar to the shape of a mule's hoof. In some cases the entire hoof is
contracted, the sole has more concavity and the frog atrophies. Some horses
develop heel bulb contraction.

RULE OF HOOF MOISTURE

Moisture content in the hoof is maintained by circulation and is influenced
by the environment. Dynamic movement of the hoof during exercise increases
the circulation within the foot (Butzow 1961). The elasticity of the hoof
is dependent on the moisture content of its keratinized structures, and lack
of moisture reduces resiliency of the hoof, affecting shock absorption (Emery
et al 1977).

(A solar view of the hoof. The schematic representation is of the area
involved in shock absorbtion. The dotted line is the area occuppied by the
quarters and heels during expansion of the hoof wall.)

The caudal part of the hoof wall functions like a spring, spreading apart
as the foot contacts the ground, absorbing the energy of impact. The outward
movement of the heels and quarters is permitted by the flexible frog, the
bars support the hoof wall and assist in their return to a non-weight-bearing
position as weight is removed. Proper function of this spring depends
on resiliency of the keratinized structures of the hoof. The dynamic movement
of the hoof wall creates a pumping action that increases circulation within
the foot (Lambert 1966).

HYPOTHESIS FOR PRIMARY CONTRACTED HEELS

Many authors (Emery et al 1977, Dollars 1898, Hays 1968, Lungwitz 1966 and
Stashak 1987) indicate concurrency of LTLH and contracted heels. Stashak
1987 recommends balancing the feet for treatment of contracted heels, indicating
that some cases can be resolved after a single trimming. The same observation
was made by this author. Increasing hoof angle by 3 to 5 degrees and balancing
the foot with the same level of activity resulted in expansion of the heels
within a few weeks. This observation led to the following hypotheses regarding
the development of primary contracted heels in the horse: lowering the heels
or LTLH increases tension on the deep digital flexor tendon (DDFT). The tension
pulls the deep digital flexor muscle (DDFM), causing it to stretch. The DDFM
opposes the stretch by contracting. The contraction of the muscle, caused
by a stretch reflex involving nerve fibers in the muscle, signal when the
muscle is suddenly stretched; the static stretch reflex continues to cause
muscle contraction as long as the muscle is maintained at excessive length
(Guyton 1986). When the LTLH condition is maintained, the muscle will continue
to oppose that force. The contraction of the DDFM pulls the caudal aspect
of the foot, and weight distribution to the heels is decreased.

(Development of contracted heels depicted diagrammatically. Contraction
of the deep digital flexor muscle (DDFM) lifts the caudal hoof, decreasing
normal weight placement to the heels (arrow). The black triangle represents
the relative weight distribution to the bottom of the hoof. The navicular
bone (NB) and the sesamoid bones (S) normally function as pulleys, for the
deep digital flexor tendon (DDFT) and may actually cause lifting of the
heels.)

During weight bearing, the heels don't reach maximal expansion; circulation
within the foot decreases and the keratinized structures lose moisture and
contract. Contraction is more rapid at the heels since the bulbs of the heels
are less resistant to the contracting forces. Contraction of the heels develops
in two planes, narrowing and curling of the hoof wall.

(To the left is shown a hoof one hour after being detached from a laminitic
case. The left bar and a circular section of the sole were removed, decreasing
the resistance to narrowing and curling of the hoof wall.)

When contraction is severe, the bulbs of the heels begin to contract.
The caudal hoof wall becomes more upright and loses the spring action of
the heels. Impact is being transmitted to bones and ligaments, increasing
the chance for limb injury.

TREATMENT

Most treatment regimens for contracted heels are aimed at treating the symptoms
and not the cause (Lambert 1966). Treatment principles include trimming and
balancing the feet and assisting heel expansion. Primary contracted heels
have to be differentiated from secondary contracted heels, caused by a painful
condition in the foot or disuse of the limb. Berns 1918 described the long-term
effect of contracted heels on a group of horses. The clinical signs were
similar to navicular disease, but after trimming and expanding the hooves,
the horses became sound.

Numerous treatment methods appear in the literature. Some can aid in the
expansion of the heels, while others can be harmful. Methods include: lowering
the heels to increase frog pressure (Simpson 1968); special steel shoes for
contracted heels (Russel 1882); springs applied against the bars and special
spreading devices (Lungwitz 1966); mushroom shoes, tips, bar shoes and pads;
beveled horseshoes (The Horseshoer1966); grooving or rasping the
hoof wall (Stashak 1987); Jenny et al 1965 recommend the use of acrylics
to treat contracted heels.

Increasing frog pressure has no effect on heel expansion, and lowering the
heels can lead to further contraction. Tip shoes are more natural to the
hoof but tend to concentrate pressure on the toe, separating the hoof wall
at the white line. Beveling the horseshoe hoof surface can aid in heel expansion,
but rasping and grooving the hoof wall can cause loss of moisture from the
hoof. Spreading devices and springs should be used with caution or avoided.

Overgrown hooves should be trimmed short, and the horse exercised daily.
Some animals may have sore feet following trimming, but will improve gradually.
Berns 1918 recommends pine tar and oakum held by a leather pad. Leaving the
horse barefoot and exercising it is another method. Acrylics can be used
to reconstruct underrun heels; a new product that uses rubber particles that
are glued to the bottom of the hoof wall may aid in heel reconstruction (Ferguson
1994).

Horses with LTLH should be trimmed every 3-4 weeks to maintain a constant
hoof angle. Rick 1907 recommends trimming the feet to establish a 53 degree
for the forelegs and a 58 degree angle for the hind legs. These figures are
higher and more correct when compared to figures measured randomly on modern-day
horses. Breed, function, conformation, gait and individual pattern of hoof
growth has to be considered when balancing the horse's hooves.

Increasing the hoof angle can resolve the condition for some of the cases,
sometimes in one treatment (Stashak 1987). Once the heels expand, the groove
formed between the bulbs of the heels opens.

Hoof moisture can be increased by dampening the paddock with water or applying
a commercial poultice, especially following trimming. Hooves afflicted with
thrush are trimmed until healthy tissue is reached and pine tar is applied
to the exposed areas.

If shoeing is required, the horseshoe nails are driven anterior to the
midquarters, and the horseshoe is fit gradually wider at the quarters and
heels, extending about two centimeters backwards to support the heels.

(An excellent example of the relationship of the horseshoe to the contracted
hoof. The hoof surface of the horseshoe was beveled to encourage heel
expansion.)

A good contact between the hoof and horseshoe is important - this will
allow uninterrupted expansion and contraction of the heels during motion.

U.S. War Department (1966) Normal, special and corrective shoeing. In: The
Horseshoer. California Polytechnic State University, San Luis Obispo,
CA. pp 70-73. ¨

Dr. Avisar is a practicing equine veterinarian in Neoth, Golan, Israel.
For 17 years before becoming a veterinarian, he worked as a farrier, including
seven years with UC Davis Veterinary School farrier, Charles A.
Heumphreus.